Lots of info (good and bad) in those threads. All of it I have read before, by the way.
Nick , how many different engines/heads were used in your test? Unless there are variations from engine to engine I see no explanation as to why so many have NOT had PTV problems with the CMS/VT Stage II's.

 

2.5 makes more top end power and needs a modified or aftermarket intake valve to work. Its the biggest cam we offer with a stock piston.

 

You pretty much don't need to even think about PTV with the TFS head. Any cam that will cause PTV with the TFS head is a 8000+ monster.

 

The variations are in the cam gears, like I said 0.005" does clear. So if your gears are straight up (about half are) or retarded slightly (about a quarter are) and/or your heads were decked before you installed them (0.008" typical retards the cam 0.5 degrees) you will clear.

I have built and pulled apart a few dozen modulars and never saw a 4.6 with the piston more than 0.018" in the hole. Most run 0.012" to 0.015". They are very tight spec engines other than the cam gears.

And finally the saving grace to this motor, the stock PI valve is the hardest material I have ever seen used in a valve and the stock pistons are pretty hard too. If you touch a 60-80's Chevy or Ford small block valve to a piston you either bend the valve or shatter the piston. On the 4.6 PI the stock valve will cut into the piston about 0.005" or so making cute little eyebrow shaped reliefs. I know of no other motor you can do this on. Aftermarket SS valves will bend a ton faster than the stock stuff since they are softer.

Like I said, get another stock motor (they are cheap enough), install a set of cams and see for yourself. If the motor makes tapping sounds right after installing a set of cams and the tapping goes away after a few minutes I would wager you now have some cute reliefs in your pistons and many have reported this from decently running engines after they took them apart.

 

So if the piston and valves are hitting, is that something a person would hear once installed? And what would those "cute" reliefs in your pistons do? I mean how would that affect the cars performance other than making notches in your pistons that you didn't want?

 

People report this "tapping" noise all the time after installing certain performance cams, funny thing as I have never heard it once myself.

The reliefs allow the valve the extra clearance it needs to operate, the reliefs themselves don't do anything to the power of the engine.

In reality we all want reliefs in our pistons as that is the main hindrance to running good cam specs for these motors. Once you install reliefs for the intake valve you can pretty much run any cam spec you want.

 

so getting some of the mhs cam gears which are closer to spec then stock and some cms stage 2's would be alright then. because the lose spec area of the engine is the gears them selves? I originally wanted the cms cams this is why I ask.

 

Thank you sir!!!

 

BTW - here is the mark the valve makes on the piston, its circled in red (and yes this piston has other problems)

 

Others may say 0.005" is "alright" but that will never come out of my mouth. I have enough trouble getting old schoolers to believe that 0.035" is enough as most engine builders are used to 0.070" minimum which was the pushrod spec for decades.